My planetary set up is a single planet with 110% Earth density, and a planetary radius of 1.4 Earths. It is a continental world composed of 89% Liquid water oceans, stretching up to 13 km at the bottom of the trenches. It has a single rocky barren moon with a mass not dissimilar to our moon.

The unique aspect I would like to introduce is another rotational axis than the regular day-night paradigm. It rotates at a proportional speed to maintain a 23.9 hour "earth-day" with its increased mass and density, but also has a strange x-axis rotation which sees the poles switch places every 250,000 years and make a full rotation to their original alignment in 500,000 years.

  1. The storytelling function of this rotation is to make a cyclical series of ice ages and global warming as the two continents {located opposite to each other relative to the surface} get dragged along to their poles and then to the equator and back again.

  2. My civilizations are very recent to the planet's timescale, and reached the neolithic at the best possible moment for development (i.e. Both continents are located in their hemisphere's respective temperate regions.) Thus, this is the first iteration of a cycle they must live through as a sapient collective.

  3. I feel like I'm missing something, astrophysics-wise, though I thought it would be a cool little story background as the civilizations dealt with the adversity of an inevitable and repetitive planetary apocalypse. If there is a principle of planetary physics that means it would eradicate all life, than I would like to be made aware of it so I could either implement the necessary changes or scrap the idea all together and go for a climate-based effect similar.

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    $\begingroup$ A rotating solid body rotates around one and only one axis; that's Euler's rotation theorem. It is geometrically impossible to for it to rotate around two axes at the same time. Geometry is rather more fundamental than physics; with physics you may argue, with geometry you may not. (And 500,000 years is an enormously long time span for a civilization; the entire history spans only about 5000 years, and even adding the Neolithic we only get about 12,000 years.) $\endgroup$
    – AlexP
    Jan 1 at 22:34
  • $\begingroup$ This saddens me greatly. Rampant natural cycles of climate change ahoy! Thanks for letting me know. = $\endgroup$ Jan 1 at 22:47
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    $\begingroup$ Don't be worried about those rampant natural cycles of climate change. In the last 500,000 years we have had three major glacial periods (Mindel, Riss and Würm in Alpine nomenclature), plus at least one almost-major one (the Younger Dryas), plus many centuries-long fluctuations, not geologically major, but definitely important for human societies. $\endgroup$
    – AlexP
    Jan 1 at 22:58
  • $\begingroup$ @AlexP - could liquid core and precession account for it? $\endgroup$
    – Stilez
    Jan 1 at 23:46
  • $\begingroup$ @AlexP "A rotating solid body rotates around one and only one axis; that's Euler's rotation theorem." The theorem says nothing about the stability of that axis. Not that it would matter much in the context, at that size/gravity of the planet it can't get so irregular a shape to cause a rampant case of the tennis racket theorem (aka Dzhanibekov effect) $\endgroup$ Jan 2 at 0:09

1 Answer 1


The main problem with this planetary setup is that the presence of a moon as big as our own will limit the amount and speed of precession of the axis of rotation that can occur. A moon acts somewhat like a gyroscope, in that it pulls its primary into alignment with it. The bigger the moon, the greater the effect, and earth's moon is pretty big... unless there is no moon, or a much, much smaller moon, the poles just aren't going to precess as much as the OP wants .

  • $\begingroup$ From what I gather the OP only devised the eccentric axis paradigm to cause climate cycles, and there is simply no need for that. The sun can easily induce an ice age or desertification period on its own. Planets are not in a steady state; we don't need to invent things that make them radically change. Nature has taken care of that. $\endgroup$
    – Vogon Poet
    Feb 16 at 14:35

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